Automotive manufacturers are increasingly forming automotive fuel tanks from polymeric materials (hereafter "plastics"), for example polyethylene, to take advantage of efficient manufacturing processes such as blow molding. Vapor venting valves are typically needed in or on the tank to vent fuel vapor from the tank. Properly sealing such valves to prevent fuel and fuel vapor from leaking to the surroundings is always an important consideration.
Valves used with plastic fuel tanks are preferably welded to the tank, for example using hot-plate welding techniques where the mating tank and valve surfaces are heated and brought into contact under a compressive force until the surfaces bond. There are two major problems associated with welding valves to the tank. First, the materials which lend themselves to being welded to plastic fuel tanks, i.e. materials similar to those used in the fuel tanks, are often not suitable for making quality vent valves because they are too soft, subject to long term creep problems, and susceptible to damage from the heat in the welding process. However, harder, higher-melting temperature plastic materials such as nylon which are suitable for use in the valve body are difficult if not impossible to weld to the plastic used for the fuel tanks. For example, polyethylene and nylon simply do not weld very well due to their different melting temperatures and other properties.
U.S. Pat. No. 5,404,907 issued to Benjey et al. illustrates one solution to the above problems by providing an efficient connection and sealing arrangement between a weldable connector portion and a non-weldable valve body.
In a first embodiment of U.S. Pat. No. 5,404,907, a standard, non-weldable vent valve includes a main valve body having a lower portion for insertion through an aperture in the fuel tank wall to extend into the fuel tank, and an upper portion positioned above the fuel tank when the valve is inserted. A weldable connector is connected to the upper portion of the valve body so that at least a portion of the weldable connector is in position for welding to the fuel tank when the vent valve is positioned in the fuel tank aperture. The weldable connector is overmolded onto the upper portion of the valve body. The valve body includes a plurality of circumferential, horizontal anti-leak ribs on its exterior. The ribs enhance the connection between the overmolded weldable connector portion and the upper portion of the valve body, and further provide a circuitous, labyrinth-type flow-restricting interface between the weldable connector and the valve body to prevent leakage of fuel and vapor between them.
Referring to FIG. 1 of U.S. Pat. No. 5,404,907, a heat-resistant vent valve body 20 has a lower portion 22 inserted through aperture 11 in fuel tank wall 10. An upper portion 24 of the valve body extends above fuel tank wall 10 and includes horizontal anti-leak ribs 34. A weldable connector 38 is overmolded on valve body 20, flowing around and between ribs 34 during the molding process to create a strong connection between them. Ribs 34 also provide a labyrinth type flow-restricting interface seal between valve body 20 and weldable connector 38 to prevent liquid fuel and fuel vapor leakage. Weldable connector 38 is welded to fuel tank wall 10 with weld feet 42 of known type.